Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.86   9.180%   $62.0797   $62.08   $62.10   $62.10  
  Purchase #2 $19.39   11.325%   $21.5859   $21.59   $21.60   $21.60  
  Purchase #3 $82.34   12.258%   $92.4332   $92.43   $92.45   $92.40  
  Purchase #4 $98.52   4.874%   $103.3219   $103.32   $103.30   $103.30  
  Purchase #5 $157.69   3.511%   $163.2265   $163.23   $163.25   $163.20  
  Purchase #6 $247.35   8.211%   $267.6599   $267.66   $267.65   $267.70  
  Purchase #7 $138.26   4.267%   $144.1596   $144.16   $144.15   $144.20  
  7 purchase totals = $800.41       $854.4667   $854.47   $854.50   $854.50